The use of riparian forest strips by small mammals in a boreal balsam fir forest

Abstract

Because riparian forest strips are perceived to buffer aquatic ecosystems from logging-related disturbance, they are usually not harvested. However, their value as refuges for terrestrial wildlife is unknown. We conducted two live-trapping experiments in the riparian zone adjacent to rivers in a boreal balsam fir ( Abies balsamea) forest in Quebec. In the first experiment, we compared late summer use, during 4 separate years, of different width riparian strips (20, 40, 60 m, and control [>300 m wide]), and different stand thinning intensities (20 m intact and 20 m thinned of 1 3 of all trees) on resident small mammals. We found no differences in the densities of the most common species, Clethrionomys gapperi and Peromyscus maniculatus, among strip types or among years ( P>0.05). We also tested for edge effects in large strips (60 m and controls). In controls, C. gapperi was less abundant in the first 20 m adjacent to the river ( P=0.004) while P. maniculatus was more abundant ( P=0.02) in that area. Neither species, however, showed an edge effect in the 60 m-strips ( P>0.10). In the second experiment, we monitored small mammals over eight consecutive weeks in a 160 m×170 m quadrat enclosing a 20 m-thinned forest strip and a clear-cut to investigate some aspects of the role of riparian strips at the landscape scale. During that time, Microtus pennsylvanicus, which was nearly absent from our study area in the previous years, invaded the clear-cuts and apparently confined C. gapperi and P. maniculatus to forest remnants such as 20 m-wide strips. A conclusion that emerges from this study and related studies on birds is that some species prefer larger strips or non-riparian habitats whereas others prefer narrow strips along riparian habitats. We recommend that managers ban the all-encompassing norms and manage for heterogeneity at different scales. Because our study was conducted at the stand scale and because it is not accompanied with an evaluation of the socio-economic aspects of riparian management, we cannot determine the proper mixture of strips in the landscape. However, our results could help managers to enhance the key-role of riparian ecosystems in maintaining regional biodiversity and contribute to the maintenance of local biodiversity by creating refuges for terrestrial wildlife.